1. Field of the Invention
This invention relates to a process for the preparation of aqueous emulsifier-free anionic polyurethane dispersions. The dispersions are prepared by reacting an organic polyisocyanate with an acrylic ester diol, a polyhydroxyl compound, and a salt of a mercaptocarboxylic acid.
2. Description of the Prior Art
Various methods are known for the production of polyurethane plastics from aqueous emulsifier-free polyurethane latices. German patent application No. 1,495,745, for instance, describes the manufacture of polyurethane plastics from polyurethane latices. The latices are produced by reacting higher molecular polyhydroxyl compounds and polyisocyanates with compounds such as taurine, 2,4-diaminobenzene sulfonic acid, .beta.-hydroxyethane sulfonic acid, tartaric acid and dispersing the resultant polyurethane materials in water. The polyurethane plastics contain 0.02 to 1 percent by weight of carboxylate groups in the polyurethane mass.
Another method for the preparation of polyurethane plastics from aqueous emulsifier-free polyurethane latices is described in German patent application No. 1,495,847. According to this disclosure, polyurethane plastics are obtained with a carboxylate group content of more than 1 percent by weight, and up to 8, preferably 7 percent by weight, of --CO.sub.2.sup.-, --SO.sub.3.sup.-, =PO.sub.2.sup.- ions in the polyurethane mass. The ionic groups are incorporated into the polyurethane by using compounds having a hydrogen atom reactive with the isocyanate and which have a group capable of forming a salt or a salt-containing group.
According to German patent application No. 1,237,306, polyurethane elastomers are prepared which, following their synthesis, are reacted with cyclic compounds such as succinic acid anhydride which either contain a salt-like group in addition to the ring (with the salt-like group being maintained during the ring-opening reaction which then gives the polyurethane masses the salt-like character), or are reacted with the cyclic compounds which acquire a group capable of forming salts by means of opening the ring and subsequently forming the salt.